This invention relates to a method and apparatus for operating an injection molding machine, and more particularly a method and apparatus for operating an injection molding machine capable of efficiently and smoothly building up the molding conditions from the start of the injection molding operation to a time at which stable molding operation can be effected in an interval in which a metal mold is exchanged and a normal operation is resumed.
Heretofore the building up interval was considered as a useless interval necessary for reaching a stable operating condition, that is an interval in which satisfactory products cannot be produced. In the building up interval, it has been the practice to perform injection molding operations of several tens of shots with constant molding conditions including injection pressures, injection speed which do not destroy the metal mold, or the operator has changed the molding conditions by manually changing injection pressures and injection speeds according to the feeling and experience of the operator. In Japanese Laid Open Patent Specification No. 189131 of 1987, there is disclosed a method of gradually changing the molding conditions from the initial condition to a stable condition by changing the molding condition for each shot by a value corresponding to a quotient obtained by dividing the difference between the values of the initial molding condition and the stable molding condition with the number of shots.
As above described, where the molding conditions during the building up interval are made constant it has been impossible to determine optimum molding conditions necessary for molding satisfactory products because it is necessary to avoid breakage of the metal mold, which results in defective products during the building up interval. Where the operator changes the molding conditions according to his feeling, good products can be obtained during the building up interval. But this method is troublesome. Moreover, the method disclosed in Japanese Laid Open Patent Specification No. 189131 of 1987 is not satisfactory and requires many shots that produce unsatisfactory products.
The inventor has made exhaustive research regarding a building up method capable of producing good products as fast as possible without relying upon the feeling or experience of the operator and found that the molding conditions enabling to obtain good products at the time of building up are dependent upon the metal mold temperature, resin temperature and the temperature of a portion of a heating cylinder just beneath a raw material supply hopper, respectively.